fix(llm): nest the theme $or under $and with the field filters — langchain-postgres rejects an operator beside field keys at the top level (500 on /search?theme=)

src/llm/search.py

@@ -78,7 +78,13 @@ def _store_filter(filters: dict[str, str]) -> dict[str, Any]:
     }
     theme = str(filters.get("theme") or "")
     if theme:
-        out["$or"] = [{f"theme_{i}": theme} for i in range(1, 4)]
+        # langchain-postgres accepts either a mapping of field keys or a
+        # single operator at the top level, never both — so field
+        # conditions and the theme $or nest under one $and.
+        theme_or = {"$or": [{f"theme_{i}": theme} for i in range(1, 4)]}
+        if out:
+            return {"$and": [*({k: v} for k, v in out.items()), theme_or]}
+        return theme_or
     return out
 
 

tests/llm/test_search.py

@@ -393,10 +393,16 @@ class TestThemeFilter:
         assert _theme_ok({}, "")
 
     def test_theme_is_pushed_down_as_an_or_of_rank_keys(self):
-        out = _store_filter({"theme": "telehealth", "doctype": "manual"})
-        assert out["doctype"] == "manual"
-        assert out["$or"] == [
-            {"theme_1": "telehealth"},
-            {"theme_2": "telehealth"},
-            {"theme_3": "telehealth"},
-        ]
+        theme_or = {
+            "$or": [
+                {"theme_1": "telehealth"},
+                {"theme_2": "telehealth"},
+                {"theme_3": "telehealth"},
+            ]
+        }
+        # field keys and an operator never share the top level (the store
+        # rejects that): fields and the theme $or nest under one $and
+        assert _store_filter({"theme": "telehealth", "doctype": "manual"}) == {
+            "$and": [{"doctype": "manual"}, theme_or]
+        }
+        assert _store_filter({"theme": "telehealth"}) == theme_or